Although James Watt did not invent the steam engine, he made improvements to already existing engines that greatly increased their power. Watt also developed several other important inventions: a rotary engine to drive machinery; a double-action engine; a steam indicator to measure pressure in an engine; and a centrifugal governor to automatically regulate engine speed. He developed the concept of horsepower to describe the operating strength of engines. Watt also made important surveys of several canal routes and invented a telescope attachment to measure distance. In 1882 the British Association named a unit of electrical power measurement after Watt.
James Watt was born on January 19, 1736, in the village of Greenock in Renfrewshire, Scotland. Watt's grandfather, Thomas, had been a teacher of mathematics, surveying, and navigation; and his father James, the treasurer and magistrate for Greenock, ran a successful business building ships, houses, and mathematical instruments. Early in his life Watt demonstrated both manual dexterity and an aptitude for mathematics, and he spent much time in his father's workshop building models of such things as cranes and barrel organs. At the age of about 18 he was sent to live in the city of Glasgow with his mother's relatives, one of whom taught at the university. Watt soon moved to London to apprentice himself to a mathematical instrument maker. Watt was a sickly young man who suffered severe headache attacks all his life, and London did not suit him. By the age of 21 he had returned to Glasgow.
Through the connections of Andrew Anderson, an old school friend, Watt received an appointment as mathematical instrument maker for the University of Glasgow in 1757 and was allowed to establish a workshop on its property. He met important professors at the university, including chemist Joseph Black (1728-1799), whose studies of the heat properties of steam led him to develop the concept of latent heat. Black and Watt remained friends and corresponded until Black's death in 1799.
In 1710 Thomas Newcomen (1663-1729) and John Calley had developed a "fire" or steam engine, examples of which were being used by the mid-1700s to pump water from mines. The university had a model of one of these Newcomen engines that needed repair, and Watt undertook the task. During the job Watt noticed that the design of this engine caused large amounts of steam to be wasted and began thinking about an engine with a separate condenser that would solve the problem. At about this time Watt met John Roebuck, founder of the Carron Works factories, who urged the young inventor to build an engine that incorporated his ideas. With the help of money from Black, Watt built a small engine to test his ideas and then entered into a partnership with Roebuck in 1768. The following year Watt obtained his most famous patent, "A New Invented Method of Lessening the Consumption of Steam and Fuel in Fire Engines."
Watt had begun his surveys for canal routes all over Scotland in 1766, and this work kept him from devoting much time to his engine. In 1772 Roebuck's went bankrupt, and Matthew Boulton (1728-1809), who had inherited the Soho Works silver factories in Birmingham from his father, assumed a share of Watt's patent. Two years later Watt left Scotland and moved to Birmingham. The partnership seemed perfect; Watt needed Boulton's financial help, and Boulton's factories needed power. The effort nearly bankrupted Boulton, but by the early 1780s Watt's engine was used in copper and tin mines in Cornwall.
During that decade, often at Boulton's suggestion, Watt continued improving his engine. In 1781 he developed a "sun-and-planet" or rotary gear that replaced the back-and-forth motion of his engine with a circular one. The following year Watt patented a double-action engine in which the pistons both pushed and pulled. Since this engine required a new method to connect the pistons, Watt created a parallel motion apparatus in which connected rods drove the pistons in perpendicular motion. In 1788 he added a centrifugal governor that controlled the engine speed, and two years later Watt invented an automatic pressure gauge. Thus, by 1790 Watt's series of improvements and inventions had moved far beyond the scope of the Newcomen engine and had created a device that powered the Industrial Revolution. In 1800 over 500 Watt engines were installed in mines and factories all over Great Britain. Watt's patents also meant that he was a very wealthy man.
Watt's interests extended beyond business and industry. In the early 1790s Watt's teenage daughter Jesse suffered from tuberculosis. His friend Erasmus Darwin (1731-1802), a physician and grandfather of Charles Darwin, attempted treatment that did not help the girl; Darwin then suggested another physician, Thomas Beddoes (1760-1808). Beddoes had a practice in the seaport of Bristol and was attempting to use inhalation of various gases to treat tuberculosis and other diseases. Despite the efforts of Beddoes, Jesse died, but he and Watt developed a partnership to further investigate the gases. The inventor designed a breathing apparatus that was manufactured briefly by Boulton's firm and distributed to various physicians around Britain who were willing to try Beddoes's treatments. In 1798 Beddoes opened the Pneumatic Medical Institute in Bristol; this facility included a clinic, classrooms, and research laboratory. In 1799 the first human experiments with nitrous oxide, or "laughing gas," were completed here; Watt, his second wife, and two of his sons all participated. Unfortunately, the experiments at Bristol were not effective in treating diseases and ended the following year.
In 1763 Watt married his cousin Margaret Miller of Glasgow; she bore him several children but died in childbirth in 1773. Two years later Watt married Ann Macgregor; she had two children by Watt and outlived him by 13 years. By 1800 Watt was essentially retired. He received numerous honors during his life, including selection as a fellow of the Royal Society in 1785 and an honorary degree from the University of Glasgow in 1806. He spent much time in his final years traveling the European continent. Watt died on August 25, 1819, at his residence Heathfield Hall outside Birmingham. Two years earlier his son James Watt, Jr., had purchased the ship Caledonia and replaced her engines, making the vessel the first steamship to leave an English port.